A missing limb of the body can be replaced by a prosthesis. The prosthesis mimics the function and/or the form of the missing limb. For the mechanical connection between prosthesis and stump of the limb, for example the shin stump or the thigh stump after amputation or exarticulation, the prosthesis comprises a so-called prosthesis shaft, which receives the limb stump and secures the prosthesis to the limb in a largely form-fitting and frictional-connecting way. Optionally, straps and similar means can also prevent the prosthesis shaft from slipping off of the limb stump.
For the fixation of the prosthesis shaft to the limb stump, a so-called liner is provided in particular, in the shape of a sock. As is known, this liner consists of an elastic material, silicone rubber or polyurethane or chloroprene-based polymer, especially RTV-silicone, a Shore A hardness of 20 to around 50. The prosthesis liner is pulled over the limb stump before putting on the prosthesis and forms a clinging, sealing and buffering intermediate layer between body and prosthesis shaft, which balances out the fitting inaccuracies which may occur in the course of the wearing and at the same time improves the wearing comfort.
In one embodiment of a prosthesis shaft, this is specifically adapted to the limb stump so that a fixation is facilitated. A frictional connection is accomplished by increasing the adhesive friction with adhesion promoting layers between the prosthesis shaft on the one hand and the skin surface of the limb stump on the other hand. One takes advantage of the fact that air is pressed out upon placing the prosthesis shaft on the limb stump, and the air can no longer flow back on account of the largely sealing action of the surfaces between limb stump and prosthesis shaft, so that an adhesion can be achieved.
An alternative but fundamentally related principle primarily takes advantage of the surface quality of the elastomer material of the liner, bringing about high friction on a skin surface of a limb, especially a hairless surface. As we know, certain elastomers such as silicone rubber or polyurethane or chloroprene-based polymers have an especially intimate adherence to the skin, especially when the elastomer is pressed against the skin surface, particularly on account of its inherent elasticity. A known prosthesis liner easily clings to the stump—with pretensioning by the naked limb stump—and it can absorb large shearing forces here. Thanks to additional means and measures, the adhering liner is mechanically connected to the rigid shaft of the prosthesis, for example by a distal metal base on the liner, which engages in a frictional-connecting and form-fitting manner with a corresponding structure on the prosthesis shaft. The prosthesis is thus held on firmly even without a vacuum forming primarily between stump and shaft.
In order to accomplish the adhesion, prosthesis liners are formed from at least one solid material layer not permeable to air, which seals off the limb stump and the inside of the prosthesis shaft from the surroundings in order to form a vacuum. The drawback to known prosthesis liners made from elastomer material is generally the intolerance of the sealing elastomer or rubber by the surface of the skin. When being worn, the inevitable activity of sebaceous and especially sweat glands in the living skin results in the detrimental formation of moisture between the skin of the limb stump and the inside of the prosthesis liner. This produces a subjective discomfort in the wearing and thus lessens the compliance in the wearing of the prosthesis which is necessary for medical purposes and for reasons of safety. On the other hand, the formation of moisture detrimentally results in a decrease in the adhesive friction between skin surface and liner, so that the risk exists of the prosthesis shaft being loosened or detached directly from the limb stump while being worn, which is associated with health risks for the prosthesis wearer, especially due to loss of control of the prosthesis, or, if applicable, of an artificial knee at the prosthesis. When walking, the risk of stumbling and falling is significantly increased. Moreover, with deficient adhesion between liner and skin surface, a usually topical but substantial frictional load occurs on the skin surface. If the skin has already been softened up by the moisture forming, skin irritation and injury may occur. Basically, the presence of moisture on the skin surface is a problem even at rest, because the skin surface is affected by this. This is highly critical especially in the case of scars or wounds. Besides general irritation and wound healing disturbance, infections of bacterial or fungal nature can also develop.